1. Field
Exemplary embodiments of the present invention relate to a technology of fabricating a semiconductor device, particularly, a semiconductor device with buried bit lines and a method of fabricating the semiconductor device.
2. Description of the Related Art
As the degree of integration of semiconductor memory devices increases, the cell structure has changed from 8 F2 or 6 F2 architecture to 4 F2 architecture to reduce the area occupied by each unit cell in a plane, where F is a minimum feature size. As described above, various methods have been used to form components, such as a transistor, bit line, word lines, and capacitor, in response to the decrease in occupied area of the unit cell. In particular, a vertical channel semiconductor device that induces vertical channel by vertically arranging a source and a drain in order to implement a 4 F2 cell structure has been developed.
In the vertical channel semiconductor device, the channel is formed perpendicular to the main surface of a substrate by forming a gate electrode around an active pillar extending perpendicular to the main surface of the substrate and forming source and drain regions above and under the active pillar around the gate electrode. Therefore, the channel length is not changed, even if the area of the semiconductor device decreases.
In more detail, a buried bit line (BBL) structure achieved by burying bit lines into a substrate under an active pillar has been developed to implement the vertical channel semiconductor device.
According to an example, buried bit lines are formed by forming a doped region by ion-implanting dopant into a substrate between active pillars and separating the doped region by etching the substrate between the active pillars. Here, resistance of the buried bit lines may be large due to physical limitation in having sufficient doping concentration.
A better method for reducing the resistance of the buried bit lines is to use metal having low resistance for the buried bit lines, but it is difficult to implement such a method. For example, a method of forming buried bit lines by forming a contact (so called, OSC (One Side Contact)) that exposes one side of an active pillar to use metal for the buried bit lines has been developed. However, the process of fabricating the buried bit lines formed in the OSC structure is complicated and the fabricating method is difficult.